Sado Red Jasper

Sado City explains that akadama-ishi is thought to have formed with the volcanic activity that created Sado's gold and silver veins, although exactly how it formed is still unclear; it occurs as veins in igneous rock. Earth-science researcher Takashi Ishibashi notes that it occurs in andesite and is found as pebbles on the coast and in rivers; it was once mined around Sugiike pond, but production has ceased, so good material is scarce. The Sado Geopark links the stone to the landslide-prone steep southern slope of the Kosado mountains, and in the great flood of 1897 (Meiji 30) many akadama stones were exposed from the ground.

Akadama-ishi is a quartz-crystal aggregate, which distinguishes it from the similar-looking local "akaishi" (赤石), a red chert; Sado City's geopark leaflet makes exactly this distinction. Its red, yellow and bluish tones correspond to hematite, limonite and clay-mineral content. Origin from Sado cannot be confirmed from appearance alone.

According to Sado City, akadama-ishi was used on Sado for arrowheads from the Jōmon period, and in the Yayoi period, when bead making flourished, it was made into tubular beads (kudatama) that have been excavated. Ishibashi adds that it is said to have been presented to Toyotomi Hideyoshi and that from the Edo period it was prized and set in gardens around Japan. In the early Edo period the Sado magistrate presented akadama stones to Edo Castle. After the 1897 flood, the money from selling the exposed stones (about 5,000 yen) was distributed to every household of Akadama village under the village rules, helping its recovery.

In Japan, akadama-ishi is regarded as a meiseki (銘石, named stone) and, according to the Sado Geopark, is counted as one of Japan's three great named stones.